The Big Bang Theory Season 4 Episode 16 : The Cohabitation Formulation
Bernadette is upset because Howard always leaves her alone right after having sex so he can help his mother in the morning. She asks Howard to move in with her, an idea that he initially turns down until he has fight with his mother. However, after listening to Howard asking her to go shopping, do the laundry and take him to the dentist, she discovers that Howard is dependent on his mother. She informs him that she will not "be his mother", to which Howard replies with an innocent "Where did that come from?". Following that, Howard is seen returning to his mother's house, where he gets grounded for running away.